Plasma steroid-binding proteins in the cysts of gross cystic disease of the breast.

Breast cyst fluids from 33 patients who underwent cyst aspiration were examined for their content of total protein, albumin, corticosteroid-binding globulin (CBG), and testosterone-estradiol-binding globulin (TeBG). Two distinct populations of cysts, based on their chloride concentration, were found. Both types of cysts had markedly reduced concentrations of the three plasma proteins compared to plasma levels. Concentrations of the proteins in the low chloride (less than 40 meq/liter) cysts were substantially lower than those in the high chloride (greater than 40 meq/liter) ones. Relative to albumin, both CBG and TeBG were excluded from low chloride cysts, whereas relative to one another, the ratios of these two steroid-binding proteins were the same as those in plasma. We conclude that there are specific mechanisms in breast cysts regulating the ingress and/or egress of CBG and TeBG.